It is well known to provide electrolytic capacitors with a hermetic seal. Typical hermetic seals comprise an annular metal ring surrounding an inner glass disc. A metal post or tube for the lead of a terminal extends perpendicularly through the glass disc and is insulated by the glass from the annular metal ring. Various structures have been proposed to isolate the hermetic seal from the “wet” interior of the capacitor containing the electrolyte, thereby preventing corrosion and degradation of performance.
Smith—U.S. Pat. No. 3,293,507 discloses a capacitor having an inner case with a bung inserted in the opening (mouth). The opening of the inner case is crimped inwardly against the sides of the bung to create a seal. The anode terminal extends through the bung and through the hermetic seal positioned in the outer case.
Langer—U.S. Pat. No. 4,254,775 discloses an assembly of batteries and capacitors in a first chamber, which is isolated from a second chamber by a hermetic seal.
Parler et al.—U.S. Pat. No. 7,274,551 B1 disclose a capacitor having a lid with a chamber therein. A hermetic seal is seated on the “dry” side of the chamber and a terminal is positioned on the “wet” side of the chamber and insulated from the lid by an elastomeric ring.
Despite prior art developments, there remains a need for an electrolytic capacitor with extended reliability at higher operating temperatures, expressed as “hours per temperature.” For example, relatively high operating temperatures, such as 125° C. or greater, can decrease the service life of a capacitor by accelerating drying out of the electrolyte. Furthermore, such operating temperatures can give rise to increased pressure within the capacitor, which in turn can lead to seal failure, corrosion and loss of electrolyte. Additionally, relatively high operating temperatures can also damage the components of the capacitor element, such as the paper spacer typically provided between layers of foil.